Electron spin-flip correlations due to nuclear dynamics in driven GaAs double dots

TL;DR

This study investigates electron spin-flip correlations in driven GaAs double quantum dots, revealing nuclear spin dynamics and the effects of spin-orbit coupling through experimental measurements and theoretical modeling.

Contribution

It provides new experimental data on spin correlations over microsecond to millisecond timescales and compares them with a theoretical model, highlighting areas of agreement and discrepancy.

Findings

Correlation peaks at zero and nuclear Larmor frequency differences

Additional peaks when spin-orbit coupling is significant

Residual correlations observed at longer timescales

Abstract

We present experimental data and associated theory for correlations in a series of experiments involving repeated Landau-Zener sweeps through the crossing point of a singlet state and a spin aligned triplet state in a GaAs double quantum dot containing two conduction electrons, which are loaded in the singlet state before each sweep, and the final spin is recorded after each sweep. The experiments reported here measure correlations on time scales from 4 $\mu$s to 2 ms. When the magnetic field is aligned in a direction such that spin-orbit coupling cannot cause spin flips, the correlation spectrum has prominent peaks centered at zero frequency and at the differences of the Larmor frequencies of the nuclei, on top of a frequency-independent background. When the spin-orbit field is relevant, there are additional peaks, centered at the frequencies of the individual species. A theoretical model which neglects the effects of high-frequency charge noise correctly predicts the positions of the observed peaks, and gives a reasonably accurate prediction of the size of the frequency-independent background, but gives peak areas that are larger than the observed areas by a factor of two or more. The observed peak widths are roughly consistent with predictions based on nuclear dephasing times of the order of 60 $\mu$s. However, there is extra weight at the lowest observed frequencies, which suggests the existence of residual correlations on the scale of 2 ms. We speculate on the source of these discrepancies.